821 research outputs found
Validity of path thermodynamics in reactive systems
Path thermodynamic formulation of nonequilibrium reactive systems is considered. It is shown through simple practical examples that this approach can lead to results that contradict well established thermodynamic properties of such systems. Rigorous mathematical analysis confirming this fact is presented
Reply to "Comment on `Validity of path thermodynamic description of reactive systems: Microscopic simulations'
The Comment's author argues that a correct description of reactive systems
should incorporate the explicit interaction with reservoirs, leading to a
unified system-reservoirs entity. However, this proposition has two major
flaws. Firstly, as we will emphasize, this entity inherently follows a
thermodynamic equilibrium distribution. In the Comment, no indication is
provided on how to maintain such a system-reservoirs entity in a
non-equilibrium state. Secondly, contrary to the author's claim, the inclusion
of system-reservoir interaction in traditional stochastic modeling of reactive
systems does not automatically alter the limited applicability of path
thermodynamics to problematic reactive systems. We will provide a simple
demonstration to illustrate that certain elementary reactions may not involve
any changes in reservoir components, which seems to have been overlooked by the
author.Comment: To appear in Physical Review
Factors Affecting Consumers' Trust Towards E-Commerce: Evidence from Jordanian Studentsâ Perspective
E-commerce has grown widely as a new mode of trading goods and service to every work and aspect of the society due to the rapid growth of the use of internet. However, consumers are still sensitive towards the trust of e-commerce. This study examines the factors that are affecting consumersâ trust towards e-commerce, with evidence from students in Jordanian university. Using the sample of 150 university students in Jordan through questionnaires, the findings indicate that there is significant effect of consumer behaviour as well as privacy and security on consumersâ trust. This study recommends that more extensive culture awareness programs should be provided by both public and private sectors in order to provide Jordanian population with needed information about e-commerce and its benefits; and also pay more attention to the security issues and communicate their actions toward ensuring secured services to their consumers. Keywords: e-commerce, consumers, trust, behaviors, security, privac
Statistical Error in Particle Simulations of Hydrodynamic Phenomena
We present predictions for the statistical error due to finite sampling in
the presence of thermal fluctuations in molecular simulation algorithms.
Specifically, we establish how these errors depend on Mach number, Knudsen
number, number of particles, etc. Expressions for the common hydrodynamic
variables of interest such as flow velocity, temperature, density, pressure,
shear stress and heat flux are derived using equilibrium statistical mechanics.
Both volume-averaged and surface-averaged quantities are considered.
Comparisons between theory and computations using direct simulation Monte Carlo
for dilute gases, and molecular dynamics for dense fluids, show that the use of
equilibrium theory provides accurate results.Comment: 24 pages postscript (including 16 figures
Fluctuations in fluids in thermal nonequilibrium states below the convective Rayleigh-Benard instability
Starting from the linearized fluctuating Boussinesq equations we derive an
expression for the structure factor of fluids in stationary convection-free
thermal nonequilibrium states, taking into account both gravity and finite-size
effects. It is demonstrated how the combined effects of gravity and finite size
causes the structure factor to go through a maximum value as a function of the
wave number . The appearance of this maximum is associated with a crossover
from a dependence for larger to a dependence for very small
. The relevance of this theoretical result for the interpretation of light
scattering and shadowgraph experiments is elucidated. The relationship with
studies on various aspects of the problem by other investigators is discussed.
The paper thus provides a unified treatment for dealing with fluctuations in
fluid layers subjected to a stationary temperature gradient regardless of the
sign of the Rayleigh number , provided that is smaller than the critical
value associated with the appearance of Rayleigh-B\'{e}nard
convection.Comment: 33 pages, 6 figures, accepted for publication: Physica
Spurious diffusion in particle simulations of the Kolmogorov flow
Particle simulations of the Kolmogorov flow are analyzed by the
Landau-Lifshitz fluctuating hydrodynamics. It is shown that a spurious
diffusion of the center of mass corrupts the statistical properties of the
flow. The analytical expression for the corresponding diffusion coefficient is
derived.Comment: 10 pages, no figure
Hydrodynamic fluctuations in the Kolmogorov flow: Linear regime
The Landau-Lifshitz fluctuating hydrodynamics is used to study the
statistical properties of the linearized Kolmogorov flow. The relative
simplicity of this flow allows a detailed analysis of the fluctuation spectrum
from near equilibrium regime up to the vicinity of the first convective
instability threshold. It is shown that in the long time limit the flow behaves
as an incompressible fluid, regardless of the value of the Reynolds number.
This is not the case for the short time behavior where the incompressibility
assumption leads in general to a wrong form of the static correlation
functions, except near the instability threshold. The theoretical predictions
are confirmed by numerical simulations of the full nonlinear fluctuating
hydrodynamic equations.Comment: 20 pages, 4 figure
Maxwellian gas undergoing a stationary Poiseuille flow in a pipe
The hierarchy of moment equations derived from the nonlinear Boltzmann
equation is solved for a gas of Maxwell molecules undergoing a stationary
Poiseuille flow induced by an external force in a pipe. The solution is
obtained as a perturbation expansion in powers of the force (through third
order). A critical comparison is done between the Navier-Stokes theory and the
predictions obtained from the Boltzmann equation for the profiles of the
hydrodynamic quantities and their fluxes. The Navier-Stokes description fails
to first order and, especially, to second order in the force. Thus, the
hydrostatic pressure is not uniform, the temperature profile exhibits a
non-monotonic behavior, a longitudinal component of the flux exists in the
absence of longitudinal thermal gradient, and normal stress differences are
present. On the other hand, comparison with the Bhatnagar-Gross-Krook model
kinetic equation shows that the latter is able to capture the correct
functional dependence of the fields, although the numerical values of the
coefficients are in general between 0.38 and 1.38 times the Boltzmann values. A
short comparison with the results corresponding to the planar Poiseuille flow
is also carried out.Comment: 31 pages, 6 figures; to be published in Physica
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